1. Field of the Invention
This invention relates to a detecting apparatus which enables to detect accurately passing of any relatively small-sized objects such as tablets, electronic parts or the like into a detecting space.
2. Description of the Prior Art
A conventional detecting apparatus is shown in FIG. 5, in which a detecting apparatus 1 comprises a casing 1a including a light collecting lens, a plurality of light emitting elements or the like, and a driving control circuit 45. Numeral 4 is a light emitting means, in which a plurality of infrared light emitting diodes 4a are disposed in a line. Numeral 41 is a light collecting means, in which are disposed a plurality of light collecting lens 41a, each of which is opposed to each light emitting diode 4a.
A detecting space 1b is formed in the center of the casing 1a and an object 7 to be detected passes through the detecting space 1b. Numeral 42 is a slit plate which is disposed across the detecting space 1b so as to oppose to the light collecting means 41. The slit plate 42 is to restrict the width of a luminous flux incident from the light collecting means 41 to enhance the detecting sensibility.
Numeral 44 is a light receiving plate which receives the luminous flux incident from the light collecting means 41 through the slit plate 42 to make a photoelectric conversion. The light receiving plate 44 is flattened and formed by silicone, photodiodes or the like. Numeral 43 is a visible light cutting filter which is formed between the slit plate 42 and the light receiving plate 44.
A driving control circuit 45 which is disposed behind the casing 1a comprises a power source circuit 45a, a circuit 45b for lighting the light emitting means 4 and a signal amplifying circuit 45c for amplifying the signal from the light receiving plate 44. The output signal of the signal amplifying circuit 45c is transmitted to a computer (not illustrated) for processing.
When the power source is switched on, all light emitting diodes 4a of the light emitting means 4 are lighted, thereby a light membrane is formed in the detecting space.
When any object 7 such as tablets, electronic parts or the like passes through the light membrane, part of the luminous flux is shaded, so that the light quantity incident to the light receiving plate 44 is varied. A slight electric variation caused as its result is amplified by the amplifying circuit 45c, thereby electric signals are outputted. The output signals are processed by the computer to detect e.g. the quantity of the objects.
Such a detecting apparatus has the following inconveniences and disadvantages:
(A) Since the light emitting means employs a large number of infrared light emitting diodes, the parts cost and their manufacturing cost are expensive. In addition, the consumption for electric power is increased, so that the running cost becomes costly. Further, it is indispensable to prevent such a large number of diodes from being heated.
(B) Since the area of the light receiving plate is considerably broad, it may be affected by any outer disturbing light or capture any noises of radiated electromagnetic waves, so that malfunctions of the present apparatus may occur frequently.
(C) By cutting part of the luminous flux incident to the light receiving plate from the light collecting lens by means of the slit plate, it is formed into a plate-type section. As a result, the most part of the luminous flux radiated from the light emitting diodes may be ineffective. Accordingly, only a small part of the luminous flux is available, so that the detecting sensibility of the light receiving plate is decreased.